[PATCH v1 0/3] Meson A1 32-bit support

[Dmitry Rokosov]

Hello Arnd,

On Mon, Feb 27, 2023 at 03:58:50PM +0100, Arnd Bergmann wrote:
> On Mon, Feb 27, 2023, at 15:28, Dmitry Rokosov wrote:
> > Hello Neil!
> >
> > On Mon, Feb 27, 2023 at 09:15:04AM +0100, neil.armstrong at linaro.org wrote:
> >
> > [...]
> >
> >> I'm aware Amlogic also runs their kernel as 32bit to gain a few kbytes
> >> of memory, but those processors are ARMv8 and the arm64 arch code
> >> has been designed for those CPUs.
> >> 
> >> So far I didn't find a single good reason to add 32bit support for
> >> ARMv8 Amlogic based SoCs, if you have a solid reason please share.
> >
> > I totally agree with you, but I suppose it's fully related to 'big'
> > Amlogic SoC like S905_ or A311_ series. A113L (aka 'a1') is
> > a cost-efficient dual-core SoC which is used for small, cheap solutions
> > with cheap components. Every cent is important during BoM development.
> > That's why usually ODMs install small ROM and RAM capacity, and each
> > megabyte is important for RAM/ROM kernel and rootfs footprints.
> > Why am I talking about rootfs? For such small projects a good
> > choice is buildroot rootfs assembling framework. Unfortunatelly,
> > buildroot doesn't support 'compat' mode when kernel and userspace have
> > a different bitness. In the internal project, we save several
> > percents of ROM/RAM free space using 32-bit configuration (mostly rootfs
> > ROM space, to be honest). Therefore, for such 'little' cost-efficient
> > SoCs we can make an exception and support 32-bit configuration, from my
> > point of view.
> >
> > What do you think about that?
> 
> I would argue that is a problem with buildroot, and using a 32-bit
> kernel is not something we should encourage over fixing buildroot
> to do it right, or building the kernel separately from the rootfs.
> 
> We do allow building support for a couple of ARMv8 SoCs in 32-bit
> mode, but that is usually because they ship with a 32-bit bootrom
> and cannot actually run a 64-bit kernel.

To be honest, I didn't know about this principle. It looks like a very
rational approach "start from max supported bitness".
Based on overall maintainers opinion, we have to prepare a patch for
buildroot to support compat mode :)

[...]

-- 
Thank you,
Dmitry